1. Field
The presently disclosed subject matter relates to an optical semiconductor device including a semiconductor light-emitting element and a Schottky diode element as an electrostatic protection element which are antiparallelly-connected to each other.
2. Description of the Related Art
Generally, in an optical semiconductor device including a semiconductor light-emitting element such as a light-emitting diode (LED) element or a laser diode (LD) element, an electrostatic discharge (ESD) protection circuit is connected between the terminals of the semiconductor light-emitting element, in order to avoid damage or destruction by ESD phenomena. Particularly, the reverse breakdown voltage of a GaN light-emitting element by applying a reverse voltage thereto is smaller than those of AlGaAs, AlGaInP or GaP light-emitting elements by applying reverse voltages thereto. Therefore, GaN light-emitting elements are easily subject to damage or destruction due to the application of a small reverse voltage thereto.
In a first prior art optical semiconductor device, a semiconductor light-emitting element and a Zener diode element as an ESD protection element are antiparallelly connected to each other, and also, are mounted on a semiconductor support substrate.
When a reverse voltage due to the ESD phenomena is applied to the first prior art optical semiconductor device, a forward current flows through the Zener diode element, so that the above-mentioned reverse voltage is not applied to the semiconductor light-emitting element. Thus, the reverse breakdown voltage of the semiconductor light-emitting element against the ESD phenomena can substantially be increased.
In the above-described first prior art optical semiconductor device, however, the mounting steps of the Zener diode element are so complex that the manufacturing cost would be increased. Also, spacing for mounting the Zener diode element is required in the semiconductor support substrate, which would increase the device in size.
In a second prior art optical semiconductor device (see: JP2011-520270 & US2011/0272728A1), a semiconductor light-emitting element is mounted on a semiconductor support substrate, and a Schottky diode element as an ESD protection element is formed in the semiconductor support substrate. Also, in this case, the semiconductor light-emitting element and the Schottky diode element are antiparallel with each other.
When a reverse voltage due to the ESD phenomena is applied to the second prior art optical semiconductor device, a forward current flows through the Schottky diode element, so that the above-mentioned reverse voltage is not applied to the semiconductor light-emitting element. Thus, the reverse breakdown voltage of the semiconductor light-emitting element against the ESD phenomena can substantially be increased.
In the above-described second prior art optical semiconductor device, since the semiconductor support substrate is connected directly to the semiconductor light-emitting element, the resistivity of the semiconductor support substrate is made low in order to suppress the forward voltage drop of the semiconductor light-emitting element.
Note that, if the resistivity of the semiconductor support substrate is high, the forward voltage drop of the semiconductor light-emitting element is increased to increase the power loss and the generated heat, which would not realize a high-power semiconductor light-emitting element.
In the above-described second prior art optical semiconductor device, however, since the resistivity of the semiconductor support substrate is low, the reverse breakdown voltage of the Schottky diode element formed by the semiconductor support substrate is decreased. Therefore, if a semiconductor light-emitting element is constructed by a GaN LED element or a series of other LED elements to have a higher forward voltage, the forward voltage drop of the semiconductor light-emitting element becomes smaller than the reverse breakdown voltage of the Schottky diode element. As a result, a current, which should naturally be supplied to the semiconductor light-emitting element, would be leaked to the Schottky diode element, thus decreasing its luminous intensity.